1. Field of the Invention
The invention comprises a hand-holdable combined spectrophotometer and gloss meter for measuring the appearance of a colored sample.
2. Description of Related Art
A few hand-holdable spectrophotometers have been in existence on the market since the late 1980s, but have yet to penetrate the marketplace significantly due to numerous factors, including high cost, lack of ruggedness, inadequate performance and weak human ergonometric factors. Much of the prior art instrumentation is aimed at limited segments of the color marketplace, such as graphic arts spectrometers which are based on older densitometer package designs. Much of the prior art instrumentation is also highly directional. In bi-directional instruments, i.e. those with 0.degree./45.degree. geometry, either the illumination system or the detection system, and preferably both, have to be very uniform and symmetric. If not, directional samples, such as corduroy fabrics, will produce significantly different measurements depending upon their rotational orientation with respect to the instrument.
Another problem with prior art hand-held spectrophotometers is that they often used pulsed xenon lamps which have an astable line structure in their output power spectra. While it is possible to use incandescent lamps due to their inherently higher stability, nevertheless, they suffer from deterioration over time and variation from measurement to measurement.
The prior art patent literature describes recent efforts to integrate color and gloss measurements into the same instruments. In particular, U.S. Pat. No. 4,678,325 entitled APPARATUS FOR MEASURING OPTICAL PROPERTIES OF PAPER issued on Jul. 7, 1987 discloses a fairly large instrument that appears to be capable of measuring both color and gloss. U.S. Pat. No. 4,886,355 entitled COMBINED GLOSS AND COLOR MEASURING INSTRUMENT issued on Dec. 12, 1989 describes a device that employs fiber optic bundles for the purpose of gathering gloss and color information from the sample. While such an approach has advantages, it also has its disadvantages, too, namely that adds additional elements to the instrument. Other prior art patents that may be relevant to the use of fiber optic bundles in the context of color and/or gloss measuring instruments include: U.S. Pat. Nos. 3,890,047; 4,040,743; 4,218,144; 4,222,064; 4,646,054; and 4,669,873. Also of possible relevance is an article entitled A REFERENCE INSTRUMENT FOR 20.degree. 60.degree. AND 85.degree. GLOSS MEASUREMENTS which appeared in Metrologia, by Springer-Verlag, Volume 16, pp 1-5, 1980.
Other U.S. patent references of possible relevance include: U.S. Pat. Nos. 3,890,049; 4,040,743; 4,218,144; 4,319,847; 4,464,054; 4,669,873; 4,678,325; 4,886,355.
The prior art does not appear to disclose a reliable hand-held combined spectrophotometer and gloss meter which is easy to use, rugged, and provides accurate, reliable measurements of sample appearance.